That would be a Glitchtop. Each one has a weakness to one of the basic elements (One may be weak against fire, another against pure physical). If you are confident you have the arsenal to deal with them, you can kill them, and they are also catchable.

If you're unsure if you can, you should generally avoid them. You can recognize when they are in the immediate area by their song. They aggro when you get too close, so you should be able to avoid most encounters simply by moving in the opposite direction.